CEA Microphone Techniques and Placement 2 — Questions and Answers
Question 1: What is the 'Blumlein pair' stereo microphone configuration?
- Two cardioid microphones crossed at 90 degrees
- Two figure-8 (bidirectional) microphones crossed at 90 degrees, capturing a wide and accurate stereo image with natural out-of-phase side information (Correct answer)
- Two omnidirectional microphones spaced 30 cm apart
- An ORTF pair with reduced capsule spacing for a narrower stereo image
Correct answer: Two figure-8 (bidirectional) microphones crossed at 90 degrees, capturing a wide and accurate stereo image with natural out-of-phase side information
A Blumlein pair uses two figure-8 microphones with their capsules coincident and angled 90 degrees to each other (±45° from center). The combination of the front and side rejection of each capsule produces a very accurate, wide stereo image with excellent mono compatibility.
Question 2: For recording a grand piano, what is the advantage of using an 'X-Y pair' placed inside the lid?
- It captures more room ambience than a spaced pair
- It provides a phase-coherent stereo image of the full keyboard range with good mono compatibility due to the coincident capsule placement (Correct answer)
- It emphasizes the low bass strings while rejecting the treble end
- It captures an omnidirectional recording of the entire room environment
Correct answer: It provides a phase-coherent stereo image of the full keyboard range with good mono compatibility due to the coincident capsule placement
An X-Y pair inside the piano lid (with the piano's lid open on the long stick or short stick) captures a direct stereo image of the keyboard width with both capsules at the same point in space, ensuring phase coherence and strong mono compatibility — important when the mix may be played in mono.
Question 3: What is 'side address' vs. 'end address' (top address) microphone orientation?
- Side-address microphones pick up from the side of the capsule (perpendicular to the body); end-address microphones pick up from the top of the body in line with the capsule (Correct answer)
- Side-address microphones are omnidirectional; end-address microphones are cardioid
- Side-address refers to the left channel in a stereo pair; end-address refers to the right channel
- End-address microphones require phantom power; side-address microphones use dynamic elements only
Correct answer: Side-address microphones pick up from the side of the capsule (perpendicular to the body); end-address microphones pick up from the top of the body in line with the capsule
Side-address (or side-fire) microphones, like most large-diaphragm condensers, have their pickup axis perpendicular to the body — the sound enters the side. End-address (top-fire) microphones, like most small-diaphragm pencil condensers and dynamic microphones, pick up from the tip/top end of the body.
Question 4: What does 'off-axis coloration' mean in microphone polar behavior?
- The difference in frequency response between the condenser and dynamic microphone types
- The change in tonal quality and frequency response when a sound source is positioned away from the main axis of the microphone (Correct answer)
- The reduction in sensitivity when a microphone is used in a high-humidity environment
- The frequency-dependent directional pattern change caused by proximity effect
Correct answer: The change in tonal quality and frequency response when a sound source is positioned away from the main axis of the microphone
Off-axis coloration describes how the frequency response of a directional microphone changes as the sound source moves away from the primary pickup axis. High frequencies are typically attenuated more at off-axis angles, causing off-axis sounds to sound dull compared to on-axis.
Question 5: When recording a loud guitar amplifier with a dynamic microphone, how does moving the microphone from the center of the speaker cone to the edge affect the sound?
- The center of the cone produces a brighter, more detailed sound; the edge produces a warmer, rounder tone with reduced high-frequency content (Correct answer)
- The edge produces a brighter sound due to direct contact with the tweeter
- Moving to the edge reduces SPL handling and risks overloading the microphone capsule
- The center and edge positions produce identical frequency response on a standard guitar speaker
Correct answer: The center of the cone produces a brighter, more detailed sound; the edge produces a warmer, rounder tone with reduced high-frequency content
The center of a speaker cone is where high-frequency dispersion is most direct and focused, producing a brighter, more aggressive tone. The edge of the cone produces a softer, warmer sound with reduced high-frequency content. Engineers adjust placement between center and edge to tune the tone.
Question 6: What is a 'boundary microphone' (PZM — Pressure Zone Microphone), and what is its primary use case?
- A microphone designed to reject all sounds arriving at angles above 45 degrees
- A microphone mounted flush against a flat surface that captures sound in the pressure zone, free from reflections and with a hemispherical polar pattern (Correct answer)
- A bidirectional microphone used for interviewing multiple subjects simultaneously
- A microphone with a built-in preamp and A/D converter designed for mounting on music stands
Correct answer: A microphone mounted flush against a flat surface that captures sound in the pressure zone, free from reflections and with a hemispherical polar pattern
A boundary microphone (PZM) is mounted on a flat surface (table, wall, floor). In the pressure zone directly adjacent to the surface, direct and reflected sound arrive in phase, resulting in a hemispherical pickup pattern free from comb filtering artifacts. They are used for conference rooms, piano recording (inside the lid on the soundboard), and theatrical applications.
CEA Microphone Techniques and Placement 2
What is the 'Blumlein pair' stereo microphone configuration?